1. Field of the Invention
The present invention relates to an assembly of a hot wall-heating furnace used in the process of manufacturing various semiconductor devices, including the CVD process and diffusion process, and a semiconductor wafer-holding jig. The present invention also relates to a process of manufacturing semiconductor devices using this assembly.
2. Description of the Related Art
Semiconductor manufacturing apparatuses using a hot wall-heating furnace are well known. For example, in the Conference of Applied Physics, (No. 55, Nagoya, Japan, Sep. 19-22, 1994), it is reported that, in rapid thermal annealing (RTA), moving a wafer between a low temperature zone and a high temperature zone, disposed respectively at the top and bottom portion of a vertical hot wall heating furnace, can obtain a better sheet resistance distribution in the wafer surface than that by using an ordinary RTA. It is also reported that in RTA, five wafers are heat-treated at a temperature of 1000xc2x0 C. for 10 seconds to produce CMOS devices by using the above-mentioned vertical heating furnace (3rd International Rapid Thermal Processing conference, RTP ""95. Aug. 30-Sep. 1, 1995, Amsterdam, Netherlands, THE EFFECTS OF RAPID THERMAL PROCESSING ON QUARTER MICRON CMOS DEVICES, pp 101-103). It is also reported that this type of furnace is suitable for use in the reflow process (4th Int. Conf. On Advanced Thermal Processing of Semiconductors-RTP, ""96, 30-33), and in the annealing of gigabit DRAM devices (4th Int. Conf., On Advanced Thermal Processing of Semiconductors, RTP ""96).
FIG. 1 shows the main structure of a vertical single wafer heating furnace having excellent temperature distribution. Referring to FIG. 1, 1 is a furnace body made of refractory or heat insulating material. 2 is a heater. 3 is a reaction chamber made of quartz. 4 is a gas introduction conduit opened at the top of the reaction chamber 3 for feeding reaction gas from the bottom portion of the furnace. 5 is a furnace floor plate. 6 is a lifting rod which is elevated and rotated in the furnace body in the heat treatment process. 7 is a wafer holding portion extended upwards obliquely from the lifting rod 6. 8 is a wafer. 9 is a claw extended horizontally from the wafer holding portion for holding the back surface of the wafer. 10 is an O-ring. 11 is an exhaust conduit opened at the bottom of the reaction chamber 3. By using a heating furnace having such a structure, the temperature distribution of the wafer 8 is influenced by the distance from the heater 2, and thus the temperature at the center of the wafer is high while the temperature in the peripheral portion is low.
In order to make the temperature distribution of the front surface of the wafer uniform, the applicant of this application has proposed a method that has been patented in the United States as U.S. Pat. No. 6,159,873. According to the patented method, thermal storage plates having substantially the same size of the wafer are disposed in the heating furnace, and are preliminarily heated to a heat-treating temperature, and then the wafer is positioned to the proximity of the thermal storage plates. By using both the heat from the heater and from the thermal storage plates, it is possible to make temperature distribution of the front surface of the wafer uniform and raise the temperature of the wafer rapidly. In the article published in the Conference of Applied Physics, Spring, 1998, the effect of the thermal storage plates has been investigated and studied by means of simulation by the inventors of said US patent.
Moreover, U.S. Pat. No. 6,159,873 disclosed several embodiments of the use of thermal storage plates as heaters. In FIG. 12 of the US patent, it is shown that the front surface of the wafer is positioned in the direct proximity of the heater that is mounted in the flat ceiling portion of the furnace. In this manner, as the wafer and the heater are positioned close to each other, the temperature distribution of the front surface of the wafer can be significantly improved.
According to the method of the US patent, since the wafer is positioned in direct proximity of the heater mounted in the ceiling portion of the furnace, the temperature distribution is improved. However, because the section of the heating furnace is circular in shape, the clean room footprint of the furnace is big. As the building cost of a clean room for accommodating a heating furnace for manufacturing semiconductor devices is high, it is desirable to reduce the clean room footprint of the heating furnace.
An object of the present invention is to provide an assembly of a heating furnace and wafer-holding jig that can significantly reduce the clean room footprint of the heating furnace.
Another object of this invention is to provide a process of manufacturing semiconductor devices using the assembly of the invention.
In the heat treatment of semiconductor wafers (hereinafter wafer(s)), if the wafers are horizontally supported in a vertical heating furnace, the footprint is larger than the surface area of the wafers. Moreover, if the wafers are held upright in a horizontal heating furnace, similarly, the footprint is larger than the surface area of the wafers. In any case, the size of the heating furnace becomes larger. In order to make the front surface of the wafer be consistent with the longitudinal axes of the furnace, i.e., the vertical axes of a vertical heating furnace or the horizontal axes of a horizontal heating furnace, the wafer-holding jig is usually assembled with the heating furnace.
It has been found by the inventors that by changing the sectional profile of the heating furnace in such a manner that the front surface of the wafer is parallel to the inner side surface of the furnace, the above objects can be attained.
Specifically, the assembly of heating furnace and semiconductor wafer-holding jig of the invention includes a furnace body made of refractory or heat insulting material; a heater disposed around the inner side surface of the furnace body; a reaction tube which forms a uniform heating zone; and a wafer-holding jig capable of holding the wafer, and advancing and retracting in the uniform heating zone along the longitudinal axes of the furnace body. The assembly of the invention is characterized in that the front surface of the wafer is held on the wafer-holding jig in such a manner that the front surface is substantially in parallel with the surface of the heater.
According to an aspect of the invention, the assembly can be applied in a vertical heating furnace or a horizontal-heating furnace.
According to another aspect of the invention, the assembly can include a plurality of thermal storage plates disposed in the uniform heating zone . The thermal storage plates are of the same size, or are smaller than the wafers, and are disposed substantially in parallel with one of the wafers or between two wafers.
According to a further aspect of the invention, the assembly of the invention can be used in rapid thermal processing (RTP) including RTA (Rapid Thermal Annealing), RTO (Rapid Thermal Oxidation), RTN (Rapid Thermal Nitriding), RTCVD (Rapid Thermal Chemical Vapor Deposition), and RT-Wet Reflowing. When the assembly of the invention is used in a RTA, the temperature of the furnace is raised or lowered at a rate of 10-150xc2x0 C./sec and kept for 0-20 seconds at the heat-treating temperature. Under the same conditions above, the assembly can be used in RTO to form thin oxide film, and in RTN to form nitride film on the silicon surface. The assembly also can be used in atmosphere of CVD gas, under the same conditions, to form a CVD film. The assembly can also be used in high temperature steam to reflow a film of BPSG. By using the assembly of the invention, RTP can be applied on 8-12 inch CVD film.
According to a further aspect of the invention, the assembly of the invention also includes a gas-introduction hollow conduit disposed along the longitudinal axes of the heating furnace. The gas-guiding hollow conduit is communicated with the wafer-holding jig. The wafer-holding jig includes a wafer-holding portion having an ejecting hole for ejecting a gas that is inert to the wafer from the gas introduction hollow conduit.